Support for studies of antibody idiotypes and variable region expression, anti-CD4 immunity, or mouse immunogenetics has been received from the following sources: Interagency agreement FDA 224-88-1351 with NCI Frederick Cancer Research Facility for cloning and sequencing of antibody variable region cDNAs. The nature of antibody diversity n the response to Ia.7 will be analyzed. Interagency agreement FDA 224-89-1317 with the National Cancer Institute for partial support of a contract mouse colony at Hazleton Laboratories America, Inc. This contract supports the breeding and quality control testing of a wide range of novel mouse strains, as well as derivation and characterization of new recombinant strains, production of hybridomas and other serological reagents, and shipping services. Mice and reagents from this contract have been made available to interested CBER investigators.